The plain old telephone system (POTS) was initially architected to carry voice data in analog form from one subscriber to another via configurable switches. Although the telephone network evolved to using a digital transport network (i.e., the Public Switched Telephone Network (PSTN)), communication on the subscriber line connecting subscribers to the central office that serves as the entry point to the PSTN is analog. The “last mile” between the subscriber and the central office was architected for analog communications in the voiceband frequency range.
Although modems were developed to enable communicating digital data using the same analog channel used to carry analog voice data, the digital data rates between the subscriber and central office were relatively low due to the constraints of operating exclusively within the voiceband region of the spectrum. Numerous communication protocol standards have since developed to enable using the POTS infrastructure for communicating digital data at higher data rates by utilizing communication bandwidth beyond the voiceband. For example, digital subscriber line (xDSL) services utilize communication bandwidth beyond and exclusive to the voiceband. As a result, xDSL services may co-exist with voiceband communications. Co-location of access to digital networks other than the PSTN at the central office enables leveraging the POTS infrastructure investment in the subscriber line.
The central offices may be retrofitted to permit sharing the subscriber line between multiple services such as voice and digital services. Typically this is accomplished by adding digital service specific linecards and a discrete component splitter for each subscriber line so that the subscriber line can be communicatively coupled to both the existing POTS linecard and the added digital service linecard. The discrete component splitters are relatively expensive and represent a significant cost for a large number of subscriber lines.
This approach permits leveraging the existing infrastructure at the central office including the existing POTS linecards through the addition of the splitters and digital services linecards rather than the replacement of equipment. However, the additional equipment consumes valuable space within the central office that might otherwise be used for POTS linecards and additional subscriber lines. Thus this approach may not be particularly desirable for new facilities when preservation of existing capital equipment is not an issue.